Starting and operating circuit for gaseous discharge lamps



Dec. 8, 1959 'r. c. RETZER I 2,916,671

STARTING AND OPERATING CIRCUIT FOR GASEOUS DISCHARGE LAMPS Filed June 6.1958 FIG. I.

United States Patent STARTING AND OPERATING CIRCUIT FOR GASEOUSDISCHARGE LAlVIP Theodore C. Retzcr, Cedar Grove, NJ., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application June 6, 1958, Serial No. 740,275 11 Claims.(Cl. 315-239) This invention relates to an energizing system for gasousdischarge devices and, more particularly, to a circuit for starting andoperating a high pressure gaseous discharge lamp of the so-calledshort-arc type.

As is well known, a higher voltage and current are required to start ashort-arc vapor discharge lamp than to operate the lamp once it has beenignited and the are stabilized or rendered self-maintaining. This is dueto the fact that the voltage applied to the lamp during the startingcycle must first reach a value at least equivalent to the sparkingpotential of the fill gas before "a gaseous discharge can be initiatedbetween the electrodes and suflicient current must also flow through thelamp to rapidly heat the rather massive electrodes to electronemittingtemperature so that the discharge thus established can be maintained bythe voltage applied to the lamp from the supply line on which the lampis normally operated. Heretofore, lamps of this character were startedby applying a series of extremely high voltage pulses to the lamp duringthe starting cycle from suitable auxiliary circuits, as disclosed inU.S. Patent Nos. 2,708,- 251 and 2,727,188 to C. M. Rively and U.S.Patent No. 2,825,005 to L. F. Bird.

While the pulse type starting systems described in the above-mentionedpatents provide the high voltages necessary to ionize and start thehigher wattage double-ended lamps, that is, those having a rating of 500watts and above in which the electrodes are sealed in oppositelydisposed stems or arms, they are rather expensive, bulky and complicatedfor use with lamps of lower wattages. In addition, due to the magnitudeof the voltage pulses which are produced such circuits are particularlyunsuited for use with the low wattage single-ended lamps recentlydeveloped and marketed because of the danger of arc-overs between thelead-in conductors or possibly within the sockets with which thesesingle-ended lamps are used.

It is accordingly the general object of the present invention to providean improved circuit for starting and operating gaseous discharge lampswhich contain an ionizable medium and require a higher starting thanoperating voltage.

Another and more specific object of this invention is to provide acircuit for starting a high pressure gaseous discharge lamp whichcircuit is not only more compact and less'complicated and expensive thanthe high voltage pulse starting systems generally employed heretoforebut is adapted to provide a controlled starting voltage capable ofigniting low-wattage short-arc discharge lamps of single-endconstruction without damaging the lamps or auxiliary equipment.

For a better understanding of the invention and the manner in which theaforesaid objects, and others which will become apparent to thoseskilled in the art to which the invention pertains as the descriptionproceeds, reference should be had to the accompanying drawing wherein; v

2,916,671 Patented Dec. 8, 1959 Fig. 1 is a schematic illustration ofone type of circuit embodying this invention;

Fig. 2 is a schematic drawing of another type of circuit similar to thatshown in Fig. 1 but incorporating means for limiting the capacitordischarge current through the lamp during the starting cycle and forcompletely disconnecting the starting circuit from the operatingcircuit; and

Fig. 3 is a side elevational view of a single-ended 250 watt short-arcmercury lamp which characterizes the type of low wattage lamp for whichthe circuit of this invention is especially adapted.

Although the principles of this invention are broadly applicable tovarious types of gaseous discharge devices which require a highervstarting potential than that required to maintain the are once it hasbeen initiated, especially those devices which require a controlledstarting voltage of a lower order of magnitude than that produced by apulse type circuit, the invention is particularly adapted for use inconjunction with high pressure shortare lamps and hence has been soillustrated and will be so described.

With specific reference to the form of the invention illustrated in Fig.1 of the drawing, a lamp 10 of the well-known mercury short-arc typecontaining an ionizable medium, such as argon or the like in combinationwith a measured amount of mercury, and having a pair of electrodes 12,at least one of which is thermionicemitting, is connected to a source ofalternating voltage 16 by means of terminals 15, conductors 13 and 14,and a line switch 17. Connected in series with the lamp 10 is a suitablecurrent limiting device such as an inductive ballast 18, as here shown,or a resistor adapted to maintain the lamp current within safe limitsduring starting and after the lamp has been lighted and is beingoperated directly from the voltage source 16. The secondary 19 of atransformer 20 is connected in series between the ballast 18 and lamp 10thereby providing in conjunction with the voltage source 16 a seriescircuit for operating said lamp after it has been lighted.Alternatively, the secondary 19 may be inserted in said series operatingcircuit on the line side of the ballast 18. One end of the transformerprimary winding 21 is connected to the conductor 13 on either the lineside of the ballast 18, as at point A as shown in Fig. 1, or at a pointbetween said ballast and the secondary 19. Connection to point A asshown in the drawing is preferred since the primary 21 will then beconnected directly across the voltage source 16, as will be hereinafterdescribed, and full line voltage will be applied to the transformer 20at all times even when lamp current begins to flow and there is avoltage drop across the ballast 18. However, on the lower wattage typelamps the circuit performed equally well with the primary 21 connectedto point A or between the ballast 18 and the transformer secondary 19.It should be noted that if the primary 21 is connected at point A itmust be electrically isolated from the secondary 19 in order to preventshort-circuiting the ballast 18 so that in this instance the transformer20 would be an isolation type transformer rather than anauto-transformer, for example. The other end of the primary 21 isconnected to one side of a switch 24, preferably a pushbutton switch,which is normally open and is, in turn,

I connected to the conductor 14 thereby providing means the lamp whenthe switch 24 is closed exceeds the sparking potential of the fill gasthereby initiating a gaseous discharge between the electrodes 12. Thus,if the conversion or turns ratio of the transformer 20 is 1 to 1 thenthe total voltage applied to the lamp 10 when the switch 24 is closedwill be twice that which would be supplied by the voltage source 16alone.

In order to increase the current flowing through the lamp 10 during thestarting cycle and thus facilitate the heating of the electrodes 12 and,in turn, decrease the time required for the arc to becomeself-maintaining, one terminal of a capacitor 22 is connected to theconductor 13 at a point on the aforesaid series operating circuitbetween the secondary 19 and lamp 10 and the other terminal of saidcapacitor is connected to a second set of contacts provided in theswitch 24 previously referred to thereby enabling said capacitor to beconnected by means of said switch directly across the lamp. Thus, whenthe switch 24 is closed the primary 21 is connected across the voltagesource 16 and the capacitor 22 across the lamp 10 whereupon the outputof the secondary 19 is applied along with the voltage from said sourceto both said capacitor and lamp. Since the capacitor 22 alone shunts thelamp 10 it immediately charges to the voltage appearing across saidlamp. Hence, when the applied alternating voltage reaches a valuesutficient to break down the gas between the electrodes 12 and an arc isstruck therebetween rendering the lamp 10 conductive, the capacitor 22discharges through said lamp to a voltage equal to the arc voltage atwhich time the current through the lamp will decrease to a valuedetermined solely by the applied voltage and ballast 18. The capacitor22 is chosen such that the increase in the current through the lamp 10incident with the discharge of said capacitor is sufiicient tosubstantially increase the temperature of the electrodes 12. If thecurrent does not continue to flow thru the lamp 10, the capacitor22'Will, so long as the switch 24 is held closed, repeatedly rechargeand then discharge through the lamp until current flows continuously, atwhich time the electrodes 12 will be at thermionic emitting temperatureand the arc voltage decreased sufficiently to permit the lamp to beoperated directly from the voltage source 16. The capacitor 22 andballast 18 are generally selected to provide a starting current of fromabout one and a half to two times the normal operating current so thatthe electrodes 12 reach thermionic-emitting temperature and the lampstarts within a predetermined period of time (a matter of seconds) afterthe starting switch 24 is actuated, otherwise excess metal will besputtered off and the electrodes which may cause early blackening of thelamp and prematurely shorten its useful life.

After the lamp 10 has started the switch 24 is released and allowed toreturn to its normally open position thereby disconnecting the primary21 and capacitor 22 from the series operating circuit and allowing thelamp 10 to operate directly from the voltage source 16 through theballast 18 and the secondary 19. Since the secondary 19 in thisembodiment of the invention remains in the operating circuit it isnecessary that the transformer-20 be designed to carry the current whichflows through the lamp 10 when it is operating normally.

In order to simplify the design and reduce the cost of the transformer20, the secondary 19 may be connected in such a manner that it is alsodisconnected from the series operating circuit along with the primary 21and capacitor 22 after the lamp 10 has been lighted. This alternativeembodiment is shown in Fig. 2 wherein a switch 24' having an additionalset of contacts 25 is provided which contacts are shorted when theswitch is in its normally open position. Said contacts 25 are connectedby means of jumper leads 26 and 27 to the conductor 13 on either side ofthe secondary 19, and the primary 21 is connected to the aforesaidconductor at either point A or between the ballast 18 and the transformer secondary 19, as above-described, thus providing means fordisconnecting both said primary and secondary from the series operatingcircuit when the switch 24' is released. The switch 24' is preferably apush-button or single-action type switch so that when it is closed itnot only temporarily and simultaneously connects the primary 21 acrossthe voltage source 16, and the capacitor 22 across the lamp 10, asdescribed above, but also inserts the secondary 19 in the seriesoperating circuit, preferably in series between the ballast 18 and thepoint on said series operating circuit at which the capacitor 22 shuntsthe lamp.

In addition to the foregoing arrangement for completely disconnectingthe starting circuit from the series operating circuit after the lamp 10has been started, a second current limiting means such as a resistor 23may be connected in series with the capacitor 22, as shown in Pig. 2, toprovide a resistor-capacitor combination for shunting the lamp 115during the starting cycle. The resistor 28 not only limits the currentthrough the lamp It to a safe value when the latter is renderedconductive and said capacitor is discharged therethrough, but since thevoltage drop across the combination will be the vector sum of the dropsacross each component, the use of a resistor boosts the voltagedeveloped across said lamp during starting to a value greater that thatwhich would be developed if only a capacitor were used.

As will be obvious, by properly designing the ballast 18 and selectingthe conversion factor of the transformer 20 as well as the values of thecapacitor 22 and resistor 28, when the latter is used, the startingvoltage and current may be varied over a considerable range fromslightly above the line voltage and normal operating current to severaltimes these values. As a specific example of one application of therelatively low range of controlled starting voltages which can readilybe obtained in accordance with the principles of this invention, thecircuits above-described have been found to be especially suited for usein conjunction with single-ended low-wattage gaseous discharge lampssuch as the 250 watt short-arc lamp 10 shown in Fig. 3. As illustrated,the lamp 10' comprises generally a well-known inner arc tube 36 ofquartz or other high temperature radiation-transmissive material whichcontains two electrodes 12, at least one of which isthermionic-emissive, a low pressure fill of an ionizable medium such asargon or the like, and a measured amount of mercury. In order to rigidlysup port the arc tube and connect it with a source of power said aretube is longitudinally mounted within a tubular outer envelope 30 bymeans of spaced lead-in conductors 33 and 34 which are sealed throughthe same end of said envelope by means of a conventional reentrant sternassembly. Proper positioning of the lamp 10' is facilitated by means ofa pre-focus type base 32 secured to the sealed end of the outer envelope30 thus providing a lamp unit similar in appearance and size to astandard incandescent type projector lamp. The space between the arctube 36 and outer envelope 30 may be evacuated or filled with an inertgas such as dry nitrogen. In either case, it has been found desirable tolimit the starting voltage applied to lamps of this construction andsize to about 400 volts maximum otherwise destructive arcs may occurbetween the lead-in support. members 33 and 34 or within the base 32 onthe socket fixture.

As a specific example of the size of the various components required fora particular case, it has been found that when a booster transformerhaving a conversion ratio of approximately 1 to 1, an microfaradcapacitor, a 20 ohm resistor, and an inductive ballast suitably designedto limit the normal operating current to approximately 8 amperes arecombined in the manner shown in Fig. 2, a starting voltage ofapproximately 256 volts will be developed across the socket terminalswhen the ,erate the lamp.

circuit is ebmaecte itea l1Q- -volt 60-cycle supply line which startingvoltage will start the illustrated 250 watt short-arc lamp in less than3 seconds without any damage whatsoever to the lamp or socket fixture ordeleterious blackening effect. The normal operating current and voltageof this particular lamp are approximately 8 amperes and 37 volts,respectively. If a microfarad condenser is used, the resistor 28 may beeliminated, as shown in Fig. 1, since theincrease in the lamp currentduring starting produced by the discharge of the condenser in this casewill not be sufficient to damage the delicate seal construction of thearc tube 36 but will still be great enough to eifect the desired heatingof the electrodes 12.

As is well known, a considerably higher voltage is required to restart ahot lamp than to start the same lamp when it is cold, that is, at roomtemperature. Hence, the voltage applied to the single-ended lamp 10 bycircuits having the aforementioned values will only start such a lampwhen it is cold. This limitation in the instant case is, however, adistinct advantage insofar as it affords a built-in safeguard againstinadvertently applying a higher starting voltage to lamps of this typein an attempt to restart a lamp while it is hot and thereby creating asituation where the lamp or socket could be seriously damaged ordestroyed by flash-overs between the internal lead-in supports or withinthe base or socket.

In the case of higher wattage or double-ended lamps where the danger ofarc-overs is not present and higher starting voltages are required,voltages of the desired magnitude may be obtained by properly matchingthe inductive ballast 18 and capacitor 22 so that they have the sameorder of reactance when they are both connected to the voltage source 16thereby providing a series resonant circuit when the starter switch 24.or 24 shown in Figs. 1 and 2, respectively, is actuated. The values ofthese reactive components may, of course, be selected to achieve eithertotal or partial resonance so that the desired voltage will be developedacross the capacitor 22, or serially arranged capacitor 22 and resistor28 combination as the case may be, and thus applied to the lamp 10during the starting cycle, care being taken to provide a resistor orother current limiting means of sufficient rating and size to limit thestarting current to a safe value. In

- this type circuit the transfonner 20 is preferably so designed that ithas a low reactance so as not to complicate the proper balancing of thecapacitive and inductive reactances, and for all practical purposes maybe permanently disconnected and eliminated from the circuit.

As will be obvious to those skilled inthe art, the invention may also beemployed to start lamps which are normally operated from a DC. powersupply by either incorporating in the starting circuit means totemporarily convert the DC. to A.C. voltage, such as a vibrator forexample, orby providing a separate A.C. voltage source for energizingthe starting circuit.

It will be apparent from the foregoing that the objects of the inventionhave been achieved insofar as a simple, more compact and inexpensivecircuit has been provided for starting and operating lamps containing anionizable medium and having thermionic-emitting type electrodes wherebya higher voltage is required to start than to op- In addition, bycombining the desirable features of a series resonant circuit with avoltage boosting-capacitor discharge arrangement an exceptionallyversatile starting circuit is provided which can supply a wide range ofprecisely controlled starting voltages thereby permitting the same basiccircuit to be used with the various types and sizes of discharge lampsnow being marketed.

While several specific embodiments of the invention have been describedin detail by way of illustration and example for the purposes of clarityand understanding in accordance with the patent statutes, it isunderstood that various changes and modifications may be made 6 withoutdeparting fromthe spirit and scope of the invention.

1613MB, p,

1. A circuit for starting a lamp containing an ionizable medium andrequiring a higher starting than operating voltage, said circuitcomprising conductor means for connecting said lamp to an alternatingvoltage source, a transformer having a primary and a secondary, acapacitor, and means including a switch for temporarily connecting saidprimary across the input side of said conductor means and said capacitoracross said lamp, and applying the output of said secondary to saidcapacitor and lamp.

2. A circuit for starting and operating a lampcontaim ing an ionizablemedium and requiring a higher starting than operating voltage, saidcircuit comprising conductor means for connecting said lamp to analternating voltage source, current limiting means connected to saidlamp through said conductor means, a transformer having a primary and asecondary, said secondary being connected inseries with said lamp andcurrent limiting means and in conjunction with said current limitingmeans and conductor means constituting a series circuit for operatingsaid lamp after it has been lighted, a capacitor, and switch means forconnecting said capacitor across said lamp, and said primary across theinput side of said conductor means.

3. A circuit for starting and operating a lamp contain-' ing anionizable medium and requiring a higher starting than operating voltage,said circuit comprising conductor means for connecting said lamp to analternating voltage source, current limiting means connected to saidlamp through said conductor means and adapted in conjunction therewithto operate said lamp after it has been lighted, a transformer having aprimary and a secondary, a capacitor, and means for connecting saidcapacitor across said lamp, said primary across the input side of saidconductor means, and said secondary in series with said current limitingmeans and lamp.

4. A circuit for starting and operating a lamp containing an ionizablemedium and requiring a higher starting than operating voltage, saidcircuit comprising conductor means for conducting said lamp to analternating voltage source, current limiting means connected to saidlamp through said conductor means, a transformer having a primary and asecondary which are electrically isolated from each other, saidsecondary being connected in series between said lamp and currentlimiting means through said conductor means thereby to provide a seriescircuit for operating said lamp after it has been lighted, a capacitor,and means including a switch for connecting said capacitor across saidlamp, and said primary across said conductor means at a point on theseries operating circuit closer to the input terminals thereof than saidcurrent limiting means.

5. A circuit for starting and operating a lamp containing an ionizablemedium and requiring a higher starting than operating voltage, saidcircuit comprising conductor means for connecting said lamp to analternating voltage source, an inductive ballast connected in serieswith said lamp through said conductor means, a low reactance transformerhaving a primary and a secondary which are electrically isolated fromeach other, said secondary being connected in series between said lampand ballast through said conductor means thereby to provide a seriescircuit for operating said lamp after it has been lighted, a capacitorand means including a switch for temporarily and simultaneouslyconnecting said capacitor across said lamp, and said primary across theinput side of said conductor means.

6. A circuit for starting and operating a lamp containing an ionizablemedium and requiring a higher starting than operating voltage, saidcircuit comprising conductor means for connecting said lamp to analternating voltage source, an inductive ballast connected in serieswith said lamp through said conductor means and in conjunction therewithproviding a series circuit to operate said lamp after it has beenlighted, a low reactance transformerhaving a primary and a secondary, acapacitor, and means including a switch for connecting said capacitoracross said lamp, said primary across the input side of said conductormeans, and said secondary in series between said ballast and lamp andcloser to said ballast than the point on said series operating circuitat which the capacitor shunts the lamp.

7. A circuit for starting-and operating a lamp containing an ionizablemedium and requiring a higher starting than operating voltage, saidcircuit comprising conductor means for connecting said lamp to analternating voltage source, a first current limiting means connected inseries with saidlarnp' through said conductor means and operable inconjunction therewith to operate said lamp after it has been lighted, atransformer having a primary and a secondary, a capacitor, a secondcurrent limiting means connected in series with saidcapacitor, and meansoperable to connect said serially arranged capacitor and second currentlimiting means across said lamp and said primary across the input sideof said conductor means, and to apply the output of said secondary tosaid serially arranged capacitor and second current limiting means andto said lamp.

8. A circuit for starting and operating a lamp containing an ionizablemedium and'requiring a higher starting than operating voltage, saidcircuit comprising conductor means for connecting said lamp to analternating voltage source, an inductive ballast connected in serieswith said lamp through said conductor means and operable in conjunctiontherewith to providea series circuit for operating said lamp after ithas been lighted, a low reactance transformer having a primary and asecondary, a capacitor having a resistor connected in series therewith,and means including a single-action multiple-contact switch fortemporarily and simultaneously connecting said capacitor-resistorcombination across said lamp at a point on the series operating circuitcloser to said lamp than said ballast, said primary across the inputside of said series operating circuit, and said secondary in said seriesoperating circuit in series with said ballast and lamp between saidballast and the point on said series operating circuit at which thecapacitor-resistor combination shunts the lamp.

9. In an energizing circuit for a lamp containing an ionizable mediumand requiring a higher starting than operating voltage, a startingcircuit comprising conductor means for connecting with a source ofalternating voltage, voltage-converting means, a capacitor, and meansincluding a switch for temporarily connecting said voltage-convertingmeans across the input side of said conductor means and said capacitoracross said lamp, and for applying the output of said voltage-convertingmeans to said capacitor'and lamp, said'voltage-converting means beingadapted and electrically oriented to increase the voltage normallyapplied to said lamp by the energizing circuit to a value suflicient toinitiate a gaseous discharge in said lamp within a predetermined timelimit after said switch is closed.

10. In an A.C. energizing circuit for a lamp containing an ionizablemedium and having at least one thermionic-emitting electrode, a startingcircuit comprising a transformer having a primary and-secondary, acapacitor, and means including a switch for connecting said primaryacross the line side of said energizing circuit, said capacitor acrosssaid lamp, and applying the output of said secondary to said capacitorand lamp thereby to increase the voltage applied to said lamp to apredetermined value such that said lamp is rendered conductive and saidcapacitor is discharged therethrough, said capacitor being of such valuethat the increase in current flowing through the lamp incident with thedischarge of said capacitor substantially increases the temperature ofthe thermionic electrode without damaging said lamp.

11. In an inductively ballasted A.C. energizing circuit for a lampcontaining an ionizable medium and having at least onethermionic-emitting electrode, a starting circuit comprising a lowreactance transformer having a primary and secondary, a capacitor havinga current limiting means in series therewith, and means including aswitch for temporarily connecting said primary across the line side ofsaidenergizing circuit, said capacitor and current limiting combinationacross said lamp at a point on said energizing circuit closer to saidlamp than the inductive ballast, and applying-the output of said secondary to said capacitor-current limiting combination and to said lamp,said capacitor being chosen ,to have the same order of reactance as theballast when said switch is closed and the capacitor is in the circuit,and said current limiting means havinga value such that the increase incurrent through the lamp incident with the discharge of said capacitorsubstantially increases the temperature of the thermionic electrodewithout damaging said lamp.

References Cited in the file of this patent UNITED STATES PATENTS1,930,123 Ewest et al. Oct. 10, 1933 1,994,305 Dorgelo Mar. 12, 19352,825,005 Bird Feb. 25, 1958 defiant..."

